Refrigerator defrost systems



Oct, 1955 R. E. TOBEY 2,719,406

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11 Claims. (Cl. 62-4) The present invention relates to a refrigerator defrost system for household refrigerators, and is particularly concerned with the automatic defrosting of a household refrigerator and disposal of the condensate water.

1One of the objects of the invention is the provision of an improved defrosting system which utilizes hot gas and circulates the hot gas through the evaporators by operating the motor compressor during the defrosting operation.

Another object of the invention is the provision of an improved defrosting system which is adapted to remove the frost from the evaporators so quickly that the frozen food and other food stored in the refrigerator are not heated to any substantial extent and are, therefore, not damaged by the defrost.

Another object of the invention is the provision of an improved condensate disposal system and improved means for eliminating the possibility of the condensate freezing in the bottom of the liner as it drains from the evaporators during the defrosting.

Another object of the invention is the provision of an improved defrosting system utilizing electric heaters in such manner that the refrigerator is safe, the heaters all being disposed in a concealed position, where they are not likely to come in contact with the fingers of the user.

Another object of the invention is the provision of an improved automatic defrosting system which is so arranged that danger of damage to the evaporators by overheating is eliminated.

Another object of the invention is the provision of an improved automatic defrosting system which is simple, effective, economical to manufacture, and which requires no attention on the part of the user to maintain the evaporators constantly in an efficient condition with respect to frost.

Another object of the invention is the provision of a defrost control having a thermal cutout which is made responsive to the complete defrosting of both evaporators.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views.

Referring to the drawings, of which there are seven sheets,

Fig. 1 is a front elevational view of a household re frigerator, shown without the door, and equipped with the present defrosting system;

Fig. 2 is a vertical sectional view, taken on the plane of the line 2 2 of Fig. 1, and showing the details of construction of the interior of the refrigerator;

Fig. 3 is a front elevational view, showing the evaporators and connecting conduits of the refrigerator;

Fig. 4 is a side elevational View, taken from the right side of Fig. 3;

Fig. 5 is a wiring diagram of the electrical system of the refrigerator and defrost system;

Fig. 6 is a simplified wiring diagram of the cold control circuit, which forms a part of Fig. 5;

Fig. 7 is a diagrammatic View showing the refrigerator 2,719,406 Patented Oct. 4, 1955 circuit for normal operation of the refrigerator and for the defrosting system;

Fig. 8 is a front elevational view of the refrigerator with shelves and other accessories removed, .showing the location of the defrost heater and the drain heater in the cabinet;

Fig. 9 is a fragmentary sectional view showing the method of attachment of the thermostat bulb to the upper evaporator;

Fig. 10 is a diagrammatic view showing the construction of the defrosting control and the circuits controlled thereby; and

Fig. l1 is a fragmentary elevational View partially broken away showing the construction of the Solenoid valve controlling the hot gas defrosting by-pass.

Referring to Figs. 1 and 2, 10 indicates in its entirety an insulated refrigerator cabinet having an outer shell 11 and an inner liner 12 separated by insulation 13, both the liner and shell having a door opening at the front or left side in Fig. 2, where the liner and shell are joined by the usual insulating breaker strips 14.

The liner supports on its side walls a pair of sheet metal guides 15, 16, each of which has a pair of Support ing flanges 17, 18 for supporting a pair of insulating partition members 19, 20 of rectangular shape, which may comprise sheets of glass or sheets of a suitable insulating plastic.

The partition members 19 and 2t) are sufficiently spaced from the side walls and baci; of the liner to permit the drainage of condensate down the walls of the liner. For example, the glass partition members may be spaced about half an inch from the back 21 of the liner 12, as Seen at Z2 (Fig. 2). The spacing of the glass partitions 19 and 20 from the side walls 23 and 24 of the liner may be substantially one fourth of an inch, as indicated by the spacing at 25 (Fig. 1).

The two glass partition members are spaced from each other, thereby providing a dead air space 26 between them; and these partition members separate the cabinet into a lower below-freezing space 27 and an upper above-freezing storage space 28.

The cabinet is provided with a suitable insulated door Z9, which is formed by an outer panel 30 and an inner panel 31 separated by insulation 32, and carrying a resilient sealing strip 33 all around the back of the door ad* jacent its outer edges, for engagement with a face flange on the front of the shell 11, to effect an air-tight closure of the cabinet.

The door may support a plurality of shelves 34, 35, 36, which are open above and toward the inside for reception of any articles to be stored on the shelves.

The lower below-freezing space 27 is cooled by means of a lower evaporator 37, which includes a substantially horizontal portion 38 and a vertical portion 39 of sheet metal, such as aluminum. The evaporator 37 is preferably arranged to slope toward the back, as shown in Fig. 2, and is supported on the back wall 21 of the liner by suitable bolts 4d and on the side wall of the liner by suitable brackets and bolts 41.

The evaporator 37 extends from side to side of the liner and is carried by the two side walls and the rear wall of the liner. Its structure is shown in Figs. 3 and 4, which also show the upper evaporator 42 (Fig. 2).

The upper evaporator comprises a rectangular sheet of metal, such as aluminum, which is provided with tubing on its outer side adjacent the liner 12, and is formed with two side wings 43, 44 that extend forwardly and backwardly on the sides of the liner, and with a rear body 45 that joins the wings and extends from side to side across the back 21 of the liner 12.

The evaporator 42 is spaced from the liner only suiciently to allow space for the tubing which it carries and is secured to the liner by a plurality of spacers and bolts utilizing apertures 46 in the wings and body. The upper evaporator 42 is disposed at the extreme top of the liner in the above-freezing storage space 28 and is actually at the warmest p'art of the cabinet space for the purpose of assuring the maintenance of all parts of the cabinet at a suitable temperature and providing a gradually increasing heat gradient from the bottom of the cabinet interior to the top.

The two evaporators are provided with tubing, which are in unrestricted communication between the evaporators through the tubing 47 (Fig. 4) which conducts refrigerant to the upper evaporator and the tubing 48 which conducts refrigerant back from the upper evap orator to a header or receiver 49 carried by the lower evaporator 37.

The course of the refrigerant and the circuit is shown in Fig. 7. The lower evaporator 37 is provided with its inlet at 50 from the capillary tube restrictor 51. From the inlet 50 the tubing extends backward to a horizontal pass 52 of tubing which extends across the front of the vertical ange 39 of the lower evaporator and curves upwardly at 53 to the bottom of the horizontal flange 38 of this evaporator.

From 53 the tubing has a rear horizontal pass 54 across the bottom of the evaporator shelf 38 and is curved forwardly at 55 and provided with a forward pass 56. Thereafter the tubing on the lower evaporator has a plurality of successive U bends 57-60 at the front, joined by the forwardly and backwardly extending passes 61-66, ending at 67 at the right side, where the tubing joins the upwardly extending tube 47, leading to the upper evaporator.

The downwardly extending tube 48 from the upper evaporator is bent laterally at 63 and extends into the end of the header or receiver 49. A suction line 69 extends into the other end of the receiver 49 and has an upwardly open tip-turned end 70 in the receiver. The suction tube 69 extends forwardly at 71 and dowib wardly at 72, where it is in heat exchange relation with the capillary tube 51. The upper evaporator has a single horizontal pass 73 located behind its wings and body adjacent the liner, and extending from the front of the right wing 44 across the body 45 and across the Vleft wing 43.

The upper evaporator tubing 73 extends upward at 74 adjacent the front edge of the left wing 43 and has another horizontal pass 75. The horizontal pass 75 extends backwardly on the left wing 43 across the body 45 of the upper evaporator and forwardly on the right wing 44, where it is turned downward at 76 and extends at 77 along the front edge of the right wing 44, and is turned backward at 7S and joined to the tubing 47.

The refrigeration system includes a motor compressor 79 having an outer housing 80, which includes motor parts in its upper space S1 and an oil surnp at 82 in its lower space. The motor shaft is directly connected to the compressor 83 located in the sump 82, and having its outlet at 84 and its suction inlet at 85. The compressor outlet 34 is connected by tube 86 to a pre-cooler condenser, comprising a sinuous tubing 87, which may be provided with fins or welded wires for increasing its heat dissipating surface.

The inlet to the pre-cooler is at its top', the hot gaseous refrigerant traveling downward and entering the motor compressor housing 80 at the top at 88. The partially condensed refrigerant is re-vaporized in cooling the motor parts; and the oil settles to the sump 82, where it is again carried to the compressor inlet through a conduit 89 and pumped with the refrigerant to lubricate the compressor.

The motor compressor housing S has an outlet at 90 in its top, which carries hot vaporized refrigerant through conduit 91 to the top of a main condenser 92. The main condenser may consist of a plurality of sinuous coils provided with heat dissipating tins or wires welded to the tubing and tending to drain downward to the outlet 93 of the main condenser.

The outlet 93 of the main condenser communicates with the capillary tube restrictor 51, which leads to the lower evaporator inlet at 50. A by-pass conduit 94 extends from the inlet 50 of the lower evaporator to the tubing 91 at 95 adjacent the main compressor outlet 90. By-pass tube 94 is closed by gravity actuated solenoid valve 96 provided with a suitable solenoid and plunger armature adapted to open the valve 96 when energized, for the purpose of effecting a defrost by circulation of hot gas.

The receiver 49 is clamped to the evaporator 37 adjacent the rear edge of its horizontal portion 38 by a plurality of clamping bands 97 riveted to the evaporator and clamped by a screw bolt and nut 98. A safety ruhber covered fuse 299 is carried by the evaporator adjacent the receiver 49; and the receiver 49 has a heater clamp 100 Welded to it on its rear side for clamping a refrigerator heater 101, which may be of the type that includes a resistance wire surrounded by heat resistive and heat insulating powder and housed in a copper or aluminum tube in heat conductive relation to the receiver 49 and the refrigerant contained therein.

As the heater 101 is disposed behind the receiver 49, it is inaccessible to the user, unless the user reaches behind the receiver, which is unlikely.

The upper evaporator 42 is provided with a thermal bulb 102, which is supported by an angle bracket 103, having one flange riveted at 104 to the evaporator, on the right wing 44, adjacent the outlet from the upper evaporator, which leads downward to the tube 48.

The angle bracket 103 has a through bore for a screw bolt 105 which is threaded into a clamping member 106 of angular form, clamping the bulb 102 to the clip or angle bracket 103.

The clip conductivity is such that the bulb 102 is warmer than the evaporator 42; and its temperature is controlled to a great extent by the cabinet air temperature. The lower evaporator 37 also supports a thermal bulb 107, which is clamped directly to the sheet metal horizontal shelf 38 adjacent the tubing outlet 67 of the lower evaporator so that this thermal bulb is responsive to a condition of full refrigeration of the lower and freezing evaporator 37.

While diagram, Fig. 7, shows sinuous coils from front to back with bulbs on the right, coils actually extend left to right with bulbs on left as in Fig. 8. Cold control for the lower evaporator is set at factory and located at top (Fig. 8) behind the breaker strip.

. Referring to Fig. 6, this is a simplified diagram showing the wiring circuit by means of which the motor compressor 79 is controlled from the line 10S by bellows actuated switches 109, 110, which are controlled by the bulbs 102, and 107, respectively. The fixed contacts of switches 109 and 110 are connected in parallel to the motor compressor 79 so that if either of these thermostatic controls calls for refrigeration, the motor compressor is operated.

In some embodiments cold control 107, 110 may be eliminated, as cold control 109, 102 for the upper evaporator will assure adequate refrigeration of both evaporators.

Referring to Fig. 8, this is a view showing the location of heaters in the refrigerator cabinet. AS previously described, the heater 101 is disposed at the back of the evaporator shelf 37, behind the receiver 49, and may comprise a heater of substantially watts. The size of such heaters is preferably reduced to a minimum, capable of accomplishing the defro-sting action, as all of the heat in the cabinet must immediately thereafter be pumped out of the cabinet by the refrigeration system. Another heater 111 is sinuously arranged with its insulating cover in heat conducting contact lwith the draining bottom 112 of the liner 12, with the diagonal lower back wall 113, and with both side walls 23 and 24 of the lower liner.

The purpose of the heater 111 is to maintain such a temperature in the lower part of the liner during defrosting that the condensate will not freeze in the lower part of the liner, but will be drained readily out of the discharge opening 114 into a lower condensate evaporating pan 115 (Fig. l).

Referring to Figs. 1 and 2, 116 indicates the lower freezer drawer, which is slidably mounted upon guides carried by the drawer and resting o-n front rollers 117 and provided with an upper pivoted door 118 spring pressed to close the space between the lower evaporator 37 and the partition members 19 and 2t).

Above the partition members the cabinet is provided with a combined meat and beverage drawer 119 of sufficient depth to receive bottles, lying horizontally and extending from side to side of the cabinet. The drawer 119 may be made of molded plastic and may be slidably mounted upon guides 120, which also support an insulating glass or plastic cover 121 slidably engaging the top of the drawer, but held by the guide brackets 120.

Above the drawer 119 the cabinet is provided with a pair of crisper drawers 122, 123, and an egg basket 124. These are slidably mounted upon guides 125, forming a rectangular frame, which is closed at the top on all sides by a rectangular frame part 126, which carries a glass or plastic cover plate 127.

The guides which support the drawers 122, 123 and egg basket 124 are, of course, open from the front; and the drawers are provided with a suitable facing plate 128 projecting downward, and serving as a handle.

Above the glass cover or partition 127 the cabinet is provided with a central frame 129, comprising a horizontal frame member 130 and a vertical column 131. The vertical column is supported upon the glass partition plate 127, while the horizontal frame member is extended into a rubber grommet 132 in the rear liner wall.

Two pivoted shelves 133 and 134 are mounted for pivotal and sliding motion on the horizontal frame member 132 and the liner wall 24 so that they may be supported in horizontal position by lugs 135 carried by the rear liner wall, or they may be pivoted downward to vertical position to make room for a whole watermelon or a large roast or fowl.

The lett side of the frame 129 and the left liner wall 123 support suitable guides 136 provided with front rollers 137 for slidably supporting a bottle basket 138, which is provided with guides 139 resting on the rollers. Above the bottle basket and suciently spaced to clear the bottles, the cabinet may be provided with a removable shelf 140 in the form of a tray, which is provided with a rectangular frame 141, upwardly projecting handles 142 on each side, and with rubber feet 143.

The frame 141 supports transverse` bars, permitting the air to pass through it, and is in turn supported upon lateral guide members 144 carried by the liner side walls 23 and 24.

The tray shelf 140 may be used for prepared frozen food, such as frozen desserts, salads, and the like, which may be first frozen in the freezer, or which may be cooled to the desired amount directly in the tray; and the tray may be removed bodily from refrigerator by sliding it forward and lifting it out by means of the two centrally located handles 142, one on each side of the tray.

Above the tray shelf 140 the cabinet may be provided with a shelf 145 extending from side to side, and comprising a rectangular frame 146 having laterally projecting front and rear lugs 147 mounted in rubber grommets 148 in the liner side walls and back wall.

The shelf 145 has transversely extending supporting bars or wires on the frame 146, permitting the passage of air; and it is supported immediately below the upper evaporator 42.

The upper evaporator 42 is secured to the liner side walls and rear wall in the upper end of the liner space, being spaced from the liner only sufliciently to provide room for the outer tubing on the evaporator. Therefore, the lower edge of the upper evaporator plate is spaced from the liner sufficiently for any drippage to fall into a drain trough 149, which has side portions 150, 151 extending along the side walls 23, 24 of the liner to a rear portion 152, all of which drain to a centrally located drain conduit 153.

During the defrosting of the upper evaporator the condensate is carried by a pipe 154 down to the condensate evaporation pan 115.

Referring to Fig. 5, this is a wiring diagram of the electrical system for controlling the operation of the refrigerator and its automatic defrost. In this diagram 155 and 156 indicate the line conductors leading to a connector 157 to be connected to the ordinary 110 volt, 60 cycle lighting circuit.

The motor compressor 81 is of the induction type, and is provided with a thermal overload switch 82. The conductor 158 from the motor compressor is connected to the common line conductor 156. The common conductor 156 has another parallel branch 160, which extends upwardly and is connected to the timer motor 161.

This is a self-starting synchronous clock motor, which operates constantly when the refrigerator is connected to line at 157.

The other line 155 extends upward in the diagram and is connected to the fixed contacts 162 and 163 of the thermostatic switches 109 and 110, which are controlled by the temperature of the upperl evaporator and adjacent air and by that of the lower evaporator, respectively.

The fixed contacts 162, 163 are joined by a conductor 164, which extends to one terminal 165 of a thermostatic switch 166, which may be of the bi-metallic type, and which controls an electric heater 167, which maintains a suitable temperature for butter storage in a separate butter compartment carried by the door 29.

The fixed contact 168 of the thermostatic switch 166 is connected by conductor 169 to one terminal of the heater. The other terminal of the heater is connected to line conductor 156. The other terminal of the timer motor 161 is connected by conductor 170 and conductor 171 to the conductor 164, which leads to the line conductor 155.

The present circuit contemplates the use of a twenty four hour defrost, in which the defrosting circuits are closed once in twenty four hours by the timer motor 161, which carries a suitable cam 172 on its shaft 173 for controlling a contact arm 174.

I desire it to be understood that any of the defrosting controlling devices which are shown in the co-pending applications of Thomas W. Duncan, Ser. No. 144,641, Ser. No. 231,185, Ser. No. 272,811, and Ser. No. 272,812, and the controls described in said applications are hereby incorporated by reference thereto.

The line conductor 156 has its upward extension 161) connected by conductor 175 to the movable contact 174, which is arranged to engage a xed contact 176 for controlling, by means of the timer 161, the defrosting action.

Fixed contact 176 is connected by conductor 177 in parallel to conductors 178 and 179. Conductor 178 extends to one terminal of a drain heater 111, the other terminal of which is connected by conductor 180 to the movable contacts 181 and 182 of the cold control thermostatic switches 109, 110.

These movable contacts 181, 182 are joined by conductor 183, which is also connected to conductor 184, extending to one lead 159 coming from the motor compressor.

The conductor 179, extending downward from the timer switch 174, 176, is connected by a conductor 184 to the defrost heater 101 for heating the receiver 49 and the refrigerant contained in the receiver, with which the heater is in heat conducting relation.

The other conductor from heater 101 is indicated at 185, containing a fuse; and it extends up to the conductor 183. Conductor 179 also extends downward to a solenoid coil 186, which is the coil of the solenoid valve controlling the by-pass of the defroster. The other terminal of the solenoid 186 is connected by conductor 187 to conductor 159, which is one of the terminals of the motor compressor.

The cabinet is also provided with a suitable lamp 188 for lighting the cabinet, one terminal of which is connected to conductor 160. The other terminal is connected by conductor 189 through a door switch 190 and conductor 191 to the conductor 170.

The explanation of the diagram is as follows: Line conductor 156 is the common side of the line which is connected to all of the elements to be energized, while line conductor 155 is the one in which various controlling devices are connected to accomplish the results desired. For example, line conductor 156 may be traced through conductor 160 to the lamp 188, which is controlled by the door switch 190 and conductor 191 lead ing back through conductors 171, 164, and 155 to the line. Whenever the door is opened, the door switch 190 is closed, lighting the lamp 188.

The butter compartment heater is likewise connected to the line conductor 156 at the right of the diagram. Heater 167 of the butter compartment is controlled by thermostat 166, which is connected by conductor 164 to line conductor 155. Thus the butter heater is in parallel with the lamp circuit and many other circuits; and the butter heater is controlled by the thermostat 166 to maintain a substantially constant temperature suitable for the preservation of butter at a temperature which does not render the butter too hard for spreading.

By-pass valve solenoid 186, defroster heater 101, and drain heater 111 are all in parallel so that they will all be energized at once during the defrosting action; and they are all controlled by the timer switch 174, 176, as follows.

The timer contact 174 is connected by conductor 175 to the conductor 160, which leads to conductor 156 at the line. The contact 176 of the timer switch is connected to conductor 177, which is connected to conductor 178, leading to the drain heater 111. The other terminal of the drain heater is connected by conductor 180, 183, which is controlled by the two thermostats 109, 110 in its connection to line conductor 155.

Thus the drain heater is controlled by both the timer switch and the thermostatic switches 109, 110. drain heater will not be energized unless the timer switch has reached the position of defrost and unless one of the thermostats 109, 110 demands refrigeration. If the time for defrost is reached by the timer when the compressor is not running, the defrost will wait until one of the cold controls 199, 110 calls for refrigeration by cutting in.

The conductor 177 is connected to conductor 179 leading to the by-pass solenoid 186, which is connected by conductor 187 to conductor 159. Thus the by-pass solenoid is controlled in a similar way by the timer switch and the two cold control switches 109, 110.

The defrost heater 101 is connected by conductor 184 to conductor 179 and to conductor 183. The defrost heater is then controlled on one side by the controlling timer switch 174, 176, which is in series with the conductor 179; and the defrost heater is controlled, on the other hand, by the two cold controls 109, 110, which are connected in series with conductor 185.

The motor compressor is connected by conductor 159 and conductor 184 to conductor 183, which is connected to the two terminals of the thermostatic switches 109 and 110.

The xed contacts 162, 163, connected by conductor 164, are also connected to conductor 155, which is one The I of the line terminals. The other line terminal 156 is connected to the motor compressor by conductor 158.

Thus the two cold controls 109, 110 are in parallel with the motor compressor; and when either thermostatic switch 109 or 110 is closed, the compressor will run, providing refrigeration as required by either of the Zones of the refrigerator.

The operation of the wiring system is as follows. When the line plug 159 is connected to the line, the timer motor 161 operates continuously. The operation of the timer motor is not dependent upon defrosting or refrigeration or any of the other conditions in the refrigerator.

The timer motor 161 closes the timer switch contacts 174, 176 once every twenty-four hours at the selected time, for example, three a. m., during the night, when no one is apt to be disturbed by the heating of the evaporators.

The timer switch 174 is provided with arrangements for closing the switch responsive to the operation of the timer motor; and the switch may be opened also responsive to the passage of time and operation of the timer motor 161. The timer is also provided with a latching arrangement for holding the defrosting contacts in the defrost condition, which contacts can be released responsive to the heating of the bulb 99, which actuates a bellows for unlatching the contacts 174, 176 and permitting them to close whenever both evaporators have been completely defrosted.

Bulb 99 (Fig. 8) is located on the lower evaporator 37 and has its capillary tube 99a extending upward on the left to the defrost control bellows 225. Instead of being located in the insulation, the capillary tube 99a is located in heat conducting engagement with tubes 47 and 48, Fig. 7, in a pressed groove or sump in the left liner wall. The capillary tube 99a is clamped to the upper evaporator at 99b and it is in contact with all parts of the evaporator circuit where frost or ice build-up is heavy.

The bellows 225 is charged with a small amount of gas and will not be actuated until all of the bulb 99 and capillary tube 99a are warm from defrosting. They will not become warm until all frost and ice have been melted from the tubes 47, 48, and the upper and lower evaporators 42, 37. Then the bellows will open the contacts 174, 176. In the event the thermal safety cutout 99 is not actuated, the defrosting circuit will be opened automatically responsive to the passage of time at contacts 174, 176 by the timer motor 161.

When the timer motor and switch 174, 176 reach the defrosting time, with a resultant closure of the contacts 174, 176, defrosting can take place, according to the present circuit, only if the compressor 81 is running responsive to either of the cold controls 109, 110. The defrosting circuit through the contacts 174, 176 is also in series with both the cold controls 109, 110 because it is desired to operate the motor compressor during defrosting, for pumping 'the hot refrigerant gas through the evaporator directly from the outlet of the compressor.

If the compressor is not running at the moment the defrost is closed at 174, 176, then the defrosting will be delayed until one of the cold controls 109, 110 is closed. Upon the closing of both the circuits through the cold controls and timer switch, the motor compressor will run, the solenoid valve in the by-pass will be opened,` the defrost heater will be energized; and the drain heater will be energized.

Thus hot refrigerant gas will be pumped directly from the compressor to the inlet of the evaporator, by-passing the main condenser and the capillary restrictor; and refrigerant will be vaporized in the receiver 49 and supplied to the inlet of the compressor, where it will be further compressed and heated and pumped into the evaporator. This will continue until all of the frost has been melted from both evaporators, the course of the refrigerant through the evaporators being the same during the defrosting action as it is during refrigeration.

As previously stated, the defrosting action may be terminated by the safety cut-out bulb 99 acting on the contacts 174, 176 or it may be terminated by the passage of time, by means of the timer motor 161 opening the contacts 174, 176.

By this time the evaporators are relatively warm; and therefore both the cold control switches 109 and 110 will be closed. Refrigeration will be resumed at once; and as soon as the defrost contacts 174, 176 have been opened the heaters 101 and 111 will be cut olf; and bypass valve solenoid 186 will be de-energized, closing the by-pass.

The size of the heaters is preferably kept to a minimum which is required for effecting a quick defrost; and the defrosting action is accomplished without substantially heating the food contents of the refrigerator.

The melted condensate from the upper evaporator 42 runs into the trough 149 and is Carried down to the evaporation pan by pipe 154, below the refrigerator. The condensate from the evaporator 37 runs down the side walls of the liner to the draining bottom 112 and goes out the discharge pipe 114 leading to the drain pan 115.

Discharge pipe may be provided with a suitable check valve, permitting7 water to run out and air from entering.

The operation of the defrosting system is described as follows: Both of the evaporators are maintained at evaporator temperatures which are below freezing, even though the upper evaporator is located in a space which it cools to a temperature that is above freezing.

The evaporators come in contact with air which enters the cabinet; and this air contains moisture in the form of vapor, which becomes condensed and takes the form of frost gathering on the plates, tubes, and receiver of the evaporators.

The upper evaporator purposely has an extended metal plate surface for the condensing of moisture so that it will reduce the humidity of the upper chamber. The lower evaporator is enclosed, but by diffusion, through the spacing between the various shelves and covers and the liner, moisture tends to gather in the form of frost on the colder evaporator, which is the lower one.

The accumulated frost is in the nature of an insulating coating, reducing the transmission of heat to the evaporator surfaces from the air; and the frost, being white in color, also tends to reduce the efficiency of the evaporator as a heat absorber. Therefore, it is necessary and desirable to remove the frost at regular intervals, before it gets so thick that it interferes with the efficiency of the system materially; and the present system is exemplified as having a timer which initiates a defrosting operation every twenty-four hours.

When the timer closes the timer switch, the heater 101 is energized to heat the refrigerant in the receiver 49, the drain heater 111 is energized to heat the bottom of the liner and prevent freezing of condensate there; and the solenoid winding 106 is energized to open the by-pass valve in the by-pass from the compressor outlet directly to the evaporator inlet.

The cold controls 109 and 110 close their circuit and demand refrigeration when either evaporator is warm; and therefore, if the cold controls are not already closed, they will soon become closed. This energizes the compressor, which runs during the defrost, and pumps the vaporized refrigerant out of the receiver 49, compresses and heats it, and delivers it to the inlet of the evaporator. The hot gaseous refrigerant is circulated through the lower evaporator' coils and carried to the upper evaporator coils, where it is in heat exchange with the coils and the evaporator plates, and the frost accumulated thereon.

The hot gaseous refrigerant becomes condensed and is delivered back to the receiver, where it is re-vaporized and again pumped and delivered in a hot condition as vapor to the evaporators. This continues until all the frost has been melted; and the timer switch is so arranged 10 that it will be opened by the timer after the passage of a predetermined calculated period of time.

This is to prevent extended heating of' the evaporators, which might damage the food contained in the refrigerator, and to terminate the defrost, even though the safety thermal cut-out should fail to operate.

lt is desirable that the defrosting action should be terminated as soon as the frost has been melted, and this is accomplished by the cutout bulb 99 and bellows 225, which open contacts 1740:, 17611.

This shuts o the defrost heater 10 and the drain heater 111 and deenergizes the solenoid coil 186, which closes the by-pass valve and places the system in condition for normal refrigeration.

The cold controls 109, then being closed because the evaporators are warmer than the freezing temperature at which they are usually maintained, the compressor will operate; and refrigeration will proceed until the evaporators are again at their normal temperatures, below freezmg.

Defrosting may be accomplished so quickly according to this method by using a small auxiliary frost heater and circulating the refrigerant by means of the compressor that the frozen food and other food in the refrigerator will not be damaged by heat.

Referring to Fig. l0, this is a diagrammatic illustration of the defrosting control with a simplified wiring diagram, showing the control of the defrosting heater, drain heater and solenoid.

In this diagram 161 indicates the self-starting synchronous timer motor having a driving pinion 200 which drives a gear 201 in a counterclockwise direction, as indicated by the arrow.

The elongated pinion 202 is rotatably mounted on the shaft 203, and is driven by means of the one-way spring pressed pawl 204 which engages the teeth of the pinion 202 to drive it, but permits the pinion 202 to advance beyond the gear 201 if actuated by the knob 205.

Pinion 202 going counterclockwise drives gear 206 clockwise, which drives gear 207 clockwise, which drives gear 208 clockwise with the shaft 209 and the combined knob and indicator 205.

The knob 205 has scale indicia for each hour of the twenty-four hours of the day, and the scale indicia are divided into a black portion for the night, numbered l to l2, while a white portion for the day is numbered l to 12.

The knob 20S operates adjacent a pointer 210 and is now set at approximately 3:00 a. m., just about to arrive at the time for defrost.

Gears 206 and 207 also drive shaft 173, and cam 172, having a drop 211 and a at dwell 212 for the defrosting period. The rest of the periphery 213 of the cam 172 is for normal operation of the refrigerator under refrigeration.

The knob 205 may be turned to the right because of the use of the pawl 204 on gear 201, and because of the freely rotating pinion 202, which can be rotated counterclockwise, snapping under the pawl 204. Thus the knob 205 can be advanced to the defrost position or it can be moved through beyond the defrost position to skip the defrost, or the defrost can be delayed as desired by manipulating the knob 205, which also moves the cam 172,

The cam 172 has a follower 214 pivoted at 215 and carrying a pair of insulating struts 216, 217. Strut 216 engages the contact 176e: and moves it to the right. Strut 217 engages the contact 174g and moves it to the right. Both these contacts are movable and are biased toward the left, urging the follower into engagement with the dwell 212 but remaining open when they are both in lefthand position.

In actual practice this timer is thus provided with two movable contact arms instead of one moving contact and one shaft as described in the wiring diagram of Fig. 5 and, therefore, a letter has been appended to the numbers.

The contact 174a extends into a slot in a pivoted latching lever 218 which is pivoted at 219. The latching lever 218 moves with the contact 174g and has a shoulder 220 engaging the end of the arm 221 on bell crank lever 222, which is pivoted at 223.

Bell crank lever 222 is urged in a counterclockwise direction by spring 224, toward the latching position, but bellows 225 expands downward when the bulb 99 is heated and moves the latching lever 222 clockwise against the spring 224, out of latching engagement. Then the shoulder 220 misses the end of the crank arm 221, and the latching lever 218 pivots clockwise under the influence of spring 174a, which is biased toward the lever 214.

The two contacts 174a and 176a control the energization of the defrost heater 101, the drain heater 111 and the solenoid 186 in this simplified diagram.

The operation of the defrosting mechanism of Fig. l is as follows:

The knob 205 is rotated constantly by the timer motor 161, like a clock driving through a train of gears, and the cam 172 is rotated at the same time. At the time set for defrosting, which depends on the location of the shoulder 211 of the cam, the follower 214 drops past the shoulder 211 to the dwell 212 of shorter radius. This permits contact 176@ to move to the left and to close with contact 174er.

Contact 17451 has not moved because it is latched by means of the latching lever 218 engaging bell crank 222, assuming that the evaporator is not warm enough to warm the bulb 99 and expand the bellows 225. If at the time the evaporator were hot, bellows 225 would be expanded and contact 174g would be unlatched and would also move to the left so that the defrost circuit would not be completed if the evaporator were hot.

The cam 172 continues to rotate during the defrosting period, and if the circuit is not cut olf earlier by the bulb 99 and bellows 225, the circuit will be cut olf by the timing cam 172 at the end of the dwell 212, when the follower 214 will again be pushed to the right by the cam, and the strut 216 will push contact 176a to the right, opening the contacts 17461 and 17651.

lf the frost is all melted from the evaporators before the end of the timed period for defrost, the bulb 99 will become heated and the bellows 225 will expand, moving bell crank 222 clockwise and removing shoulder 220 from latching lever 218.

Latching lever 213 can then move clockwise under the influence of spring 17451 which is biased to the left. Contact 174e then opens the circuit by moving away from contact 176a.

Assuming that the defrost has been terminated by means of the` bulb 99 becoming warm before the time defrost period has ended, the cam 172 will continue to rotate clockwise, and when the follower 214 passes off the dwell 212, follower 214 will be moved to the right, moving both the contacts toward the right to the position shown in Fig. l0 and latching the contact 174cz, as shown in that figure.

The contacts are then in open position, opening all the defrosting circuits, and the refrigerator is ready to proceed with refrigeration while the follower 214 is engaging the periphery 213 of the cam.

It will thus be observed that the defrost is initiated by the clock at a predetermined time, but is terminated by the thermostat as soon as it is completed, but if the thermostat should fail the defrost will nevertheless be terminated by the clock.

Referring to Fig. ll, this is a side elevational view, partially broken away, showing the solenoid 186 and bypass valve 96, which it controls. This solenoid actuated valve includes a coil 186 mounted upon a spool 230 of insulating material; and the spool is mounted within a rectangular frame 231 having an end piece 232.

The frame 231 is U-shaped and has an end yoke 233 and a pair of lateral legs 234, 235. This frame is made of 12 paramagnetic material, such as soft iron; and it conducts the external flux which is generated by the coil 186 out of one end of the solenoid and back to the other end.

The spool 230 may have a tube 236 of nonrnagnatic material, such as brass, which projects through the spool and extends outwardly at its upper end. The tube 236 is closed at its upper end by a headed member 237, which is supported on a horizontal arm 238 of a supporting bracket 239, which also extends across the top of the spool and has an attaching flange 240, by means of which the assembly can be mounted on the refrigerator.

The end pieces 233 and 232 of the magnetic frame have apertures to pass the tube 236, which may also extend Y below the spool 230. At its lower end the tube 236 fits on the reduced end 241 of a valve housing 242. The valve housing 242 has an internal bore 243, which may be tapered toward the top and is adapted to receive the armature plunger 244 and the valve 96.

The armature plunger 244 comprises a cylindrical member of paramagnetic material, such as soft iron, or the armature may be polarized by being made of Alnico and magnetized. The armature 244 supports a stop rod 245 at its upper end for engaging the headed member 237, which closes the upper end of the tube.

The lower end of the tube 236 projects sufficiently so that the armature may be disposed below the coil 186, when it is in deenergized position and the valve is closed by gravity. The armature 244 may have a reduced extension 246, which is readily receivable in the bore 243, and which carries the valve 96 by means of a valve stem 247.

The valve 96 may comprise a cylindrical member of suitable metal, such as stainless steel, having a conical point by means of which it is self-centering in the valve seat 248. The armature has sufficient clearance with the sides of the tube 236 to permit the valve to find a central position.

The valve housing 242 has a lateral bore 249, in which a tube 250 is secured; and it has an axial bore 251 in which a tube 252 is secured. The tubes 250 and 252 are parts of the by-pass conduit 94, which contain the by-pass valve 96 in Fig. 7. At its lower end the valve housing bore 243 may frictionally support an annular valve seat 248, which may have a cylindrical bore for receiving the valve 96.

The operation of the by-pass valve of Fig. ll is as follows: When the solenoid coils 186 are not energized, the valve rests by gravity in the closed position; and the tube 250 preferably leads to the compressor so that the valve keeps the by-pass closed until the solenoid is energized.

The tube 252 leads to the point 50, representing a point of slightly less pressure. When the coils 196 are energized for a defrost, they generate magnetic ilux, which passes out one end of the spool and inward at the other end, utilizing the frame 231 of soft iron, which presents the easiest magnetic path. The armature 244 is drawn upward in the tube to a central position, where it conducts a maximum llux; and the valve 96 is opened, which condition continues until the coils 186 are deenergized and the valve is closed by gravity.

My method of defrosting the evaporators of a refrigeration system comprises operating the motor compressor during the defrosting operation to circulate hot refrigerant in the system, while by-passing the refrigerant in a hot gaseous form directly from the outlet of the motor compressor around any and all condensers and capillary restrictors directly to the evaporator inlet.

My method includes the heating of the refrigerant in a receiver carried by the evaporator preliminary to its entry into the inlet of the motor compressor so that hot gaseous refrigerant is supplied to the inlet of the motor compressor; and there is no possibility of liquid refrigerant getting into the motor compressor.

The hot gaseous refrigerant, according to my method, is passed through the evaporators in heat exchange with the tubing and the plates of the evaporators and with the frost on the exterior surfaces of the plates and tubing and receiver to supply the heat necessary to melt the accumulated frost. This condenses at least a portion of the hot gaseous refrigerant, which is returned to the receiver, where it is heated by an electric heater that is in heat exchange relation with the receiver and with the liquid refrigerant therein, as the heater is located near the bottom of the receiver.

The refrigerant in the receiver, which has been returned, is revaporized and supplied to the compressor, which continues to pump hot refrigerant in a gaseous form from the receiver to the evaporators until the frost has been removed to a desired degree.

When the frost has been removed from both evaporators and all ice or frost has been melted from the capillary tube 99a and tubes 47, 4S which it contacts, the thermal cutout 99 opens the defrost timer contacts.

My method then includes the immediate closing of the by-pass and the deenergizing of the receiver heater and the resumption of normal operation of the refrigerator to cool the evaporators below freezing.

My method also includes the heating of the bottom drain pan of the liner, as this drain pan is located in the below-freezing zone and might otherwise be so cold that condensate running into it might be frozen.

My method includes the gathering of the condensate from an upper evaporator in a trough, which conducts it to a pipe leading to a condensate evaporation pan, and also the gathering of condensate in the lower part of the liner, and the discharge of said condensate into the same pan, where the condensate water is evaporated by the passage of air over it and around the pan.

According to my method, the defrosting may be accomplished so quickly that the food contained in the refrigerator in any of its storage zones is not adversely affected. The amount of condensate which accumulates during a single days operation may readily be evaporated from an open evaporation pan located adjacent the motor compressor.

Thus the operation of defrosting is carried on automatically without necessity for any attention; and the evaporator surfaces are maintained in an efficient condition, clean of frost, without any attention on the part of the user.

The defrosting control is provided with a control knob, which rotates and contains the indicia showing the hours of the day so that a defrost may be accomplished whenever desired by turning the knob to the position of three a. m. The defrost may be terminated or skipped by turning the defrost knob past the three a. m. position sufficiently to open the timer contacts again; and thus the defrosting operation is always under the control of the user.

While l have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, what l claim as new and desire to secure by Letters Patent of the United States, is:

l. In a defrosting system, an insulated cabinet having a cooling evaporator for a food storage zone and a colder freezer' evaporator for a below-freezing zone, a receiver carried by said freezer evaporator, said evaporators and receiver having connecting tubing in unrestricted communication with each other, a compressor, a condenser, and a capillary tube connected in this order, said capillary tube being connected to said freezer evaporator, which is connected to said cooling evaporator, and said cooling evaporator being connected to said receiver, a suction tube from an upper part of said receiver to said cornpressor, and a by-pass tube from said compressor to said freezer evaporator, by-passing said condenser and capillary tube, a solenoid valve biased to closed position in said by-pass tube, a thermostatic cold control switch having a bulb, controlling said compressor responsive to temperature of one of said evaporators, an electric heater in heat conducting contact with said freezer evaporator and receiver, heating the colder evaporator, which gathers more frost, and vaporizing and heating the refrigerant in said receiver, electrical control means for energizing said heater and solenoid valve simultaneously, the heater heating the freezer evaporator and its thermostatic switch bulb, causing the compressor to run and to deliver the hottest refrigerant irst to the freezer evaporator, having the most frost, and thence to the other warmer evapora tor having the least frost, and back to vthe receiver and compressor to melt all the frost olf the evaporators in a minimum amount of time, before the temperature of products in the cabinet is materially affected by the heat.

2. ln a defrosting system, an insulated cabinet having a cooling evaporator for a food storage zone and a colder freezer evaporator for a below-freezing zone, a receiver carried by said freezer evaporator, said evaporators and receiver having connecting tubing in unrestricted communication with each other, a compressor, a condenser, and a capillary tube connected in this order, said capillary tube being connected to said freezer evaporator, which is connected to said. cooling evapo rator, and said cooling evaporator being connected to said receiver, a suction tube from an upper part of said receiver to said compressor, and a by-pass tube from said compressor to said freezer evaporator, by-passing said condenser and capillary tube, a solenoid valve biased to closed position in said by-pass tube, a thermostatic cold control switch having a bulb, controlling said compressor responsive to temperature of one of said evaporators, an electric heater in heat conducting contact with said freezer evaporator and receiver, heating the colder evaporator, which gathers more frost, and vaporizing and heating the refrigerant in said receiver, electrical control means for energizing said heater and solenoid valve simultaneously, the heater heating the freezer evaporator and its thermostatic switch bulb, causing the compressor to run and to deliver the hottest refrigerant first to the freezer evaporator, having the most frost, and thence to the other warmer evaporator having the least frost, and back to the receiver and compressor to melt all the frost olf the evaporators in a minimum amount of time, before the temperature of products in in the cabinet is materially affected by the heat, the said cabinet having a plurality of shelves, drawers, and baflies, all of said shelves, drawers, and baies, and said evaporators being spaced from the inner Wall of said cabinet so that condensate on said wall may run down to a bottom drain aperture.

3. In a defrosting system, an insulated cabinet having a cooling evaporator for a food storage zone and a colder freezer evaporator for a below-freezing zone, a receiver carried by said freezer evaporator, said evaporators and receiver having connecting tubing in unrestricted communication with each other, a compressor, a condenser, and a capillary tube connected in this order, said capilliary tube being connected to said freezer evaporator, which is connected to said cooling evaporator, and said cooling evaporator being connected to said receiver, a suction tube from an upper part of said receiver to said compressor, and a by-pass tube from said compressor to said freezer evaporator, bypassing said condenser and capillary tube, a solenoid valve biased to closed position in said by-pass tube a thermostatic cold control switch having a bulb, controlling said compressor responsive to temperature of one of said evaporators, an electric heater in heat conducting contact with said freezer evaporator and receiver, heating the colder evaporator, which gathers more frost, and vaporizing and heating the refrigerant in said receiver, electrical control means for energizing said heater and solenoid valve simultaneously, the heater heating the freezer evaporator and its thermostatic switch bulb, causing the compressor to run and to deliver the hottest refrigerant first to the freezer evaporator, having the most frost, and thence to the other warmer evaporator having the least frost, and back to the receiver and compressor to melt all the frost off the evaporators in a minimum amount of time, before the temperature of products in the cabinet is materially affected by the heat, the said cabinet having a plurality of shelves, drawers, and baffles, all of said shelves, drawers, and baffles, and said evaporators being spaced from the inner wall of said cabinet so that condensate on said wall may run down to a bottom drain aperture, and a second electric heater arranged about said bottom drain aperture and simultaneously connected in circuit with the defrosting heater to maintain free flowing conditions for the condensate out of the bottom of the cabinet.

4. In a defrosting system for household refrigerators, the combination of an insulated cabinet provided with an insulated door, the said cabinet having its interior separated into a lower below-freezing zone and an upper above-freezing zone by a plurality of insulating barriers, a below-freezing evaporator shelf located in the lower zone and provided with freezing coils and with a receiver, a second evaporator located in the uppermost portion of the above-freezing zone and provided with a plurality of passes of coils located adjacent the side walls and back of the cabinet, the said evaporators being in unrestricted communication with each other, a motor compressor located in the lowermost portion of said cabinet on the outside, a preliminary cooling condenser connected directly to the outlet of the compressor and leading back to the top of the motor compressor housing, a main condenser connected to a top outlet of the motor compressor housing and connected at its other end to a restrictor, said restrictor leading to the inlet of the lowermost evaporator, conduits connecting the lowermost evaporator to the coils of the upper evaporator and a conduit connecting the 11pper evaporator with said receiver, a suction conduit leading from said receiver to the compressor inlet, a bypass conduit extending from said top outlet to the evaporator inlet, electric heater means in heat exchange relation with said receiver and with the refrigerant therein, valve means for normally closing said bypass and electrical control means for simultaneously energizing said receiver heater, for opening said valve in said by-pass and for running the motor compressor,

the motor compressor pumping hot gaseous refrigerant directly from the compressor to said evaporator continuously and receiving hot gaseous refrigerant from said receiver continuously, the hot gaseous refrigerant being passed through the evaporators in heat exchange relation with the coils of said evaporators and with the frost carried by said evaporators on the exterior surfaces thereof to melt the accumulated frost, the defrosting action being continued until the frost has been removed to a desired degree.

5. In a defrosting system for household refrigerators, the combination of an insulated cabinet provided with an insulated door, the said cabinet having its interior separated into a lower below-freezing zone and an upper above-freezing zone by a plurality of insulating barriers, a below-freezing evaporator shelf located in the lower zone and provided with freezing coils and with a receiver, a second evaporator located in the uppermost portion of the above-freezing zone and provided with a plurality of passes of coils located adjacent the side walls and back of the cabinet, the said evaporators being in unrestricted communication with each other, a motor compressor located in the lowermost portion of said cabinet on the outside, a preliminary cooling condenser connected directly to the outlet of the compressor and leading back to the top of the motor compressor housing, a main condenser con- 16 nected to a top outlet of the motor compressor housing and connected at its other end to a restrictor, said restrictor leading to the inlet of the lowermost evaporator, conduits connecting the lowermost evaporator to the coils of the upper evaporator and a conduit connecting the upper evaporator with said receiver, a suction conduit leading from said receiver to the compressor inlet, a bypass conduit extending from said top outlet to the evaporator inlet, electric heater means in heat exchange relation with said receiver and with the refrigerant therein, valve means for normally closing said by-pass and electrical control means for simultaneously energizing said receiver heater, for opening said valve in said by-pass and for running the motor compressor, the motor compressor pumping hot gaseous refrigerant directly from the compressor to said evaporator continuously and receiving hot gaseous refrigerant from said receiver continuously, the hot gaseous refrigerant being passed through the evaporators in heat exchange relation with the coils of said evaporators and with the frost carried by said evaporators on the exterior surfaces thereof to melt the accumulated frost, the defrosting action being continued until the frost has been removed to a desired degree, said electrical control means including an electric heater arranged outside the bottom of the liner of said cabinet to prevent the freezing of condensate and said electric heater being energized during the s defrosting action.

6. In a defrosting system for household refrigerators, the combination of an insulated cabinet provided with an insulated door, the said cabinet having its interior separated into a lower below-freezing zone and an upper above-freezing zone by a plurality of insulating barriers, a below-freezing evaporator shelf located in the lower zone and provided with freezing coils and with a receiver, a second evaporator located in the uppermost portion of the above-freezing zone and provided with a plurality of passes of coils located adjacent the side walls and back of the cabinet, the said evaporators being in unrestricted communication with each other, a motor compressor located in the lowermost portion of said cabinet on the outside, a preliminary cooling condenser connected directly to the outlet of the compressor and leading back to the top of the motor compressor housing, a main condenser connected to a top outlet of the motor compressor housing and connected at its other end to a restrictor, said restrictor leading to the inlet of the lowermost evaporator, conduits connecting the lowermost evaporator to the coils of the upper evaporator and a conduit connecting the upper evaporator with said receiver, a suction conduit leading from said receiver to the compressor inlet, a bypass conduit extending from said top outlet to the evaporato-r inlet, electric heater means in heat exchange relation with said receiver and with the refrigerant therein, valve means for normally closing said by-pass and electrical control means for simultaneously energizing said receiver heater, for opening said valve in said by-pass and for running the motor compressor, the motor compressor pumping hot gaseous refrigerant directly from the compressor to said evaporator continuously and receiving hot gaseous refrigerant from said receiver continuously, the hot gaseous refrigerant being passed through the evaporators in heat exchange relation with the coils of said evaporators and with the frost carried by said evaporators on the exterior surfaces thereof to melt the accumulated frost, the defrosting action being continued until the frost has been removed to a desired degree, said control means including a thermostatic switch for each evaporator controlled by a bulb carried by each evaporator, the said thermostatic switches being connected in parallel to the motor compressor so that the compressor is operated when either of said thermostatic switches demands refrigeration.

7. In a defrosting system for household refrigerators, the combination of an insulated cabinet provided with an insulated door, the said cabinet having its interior separated into a lower below-freezing zone and an upper above-freezing zone by a plurality of insulating barriers, a below-freezing evaporator shelf located in the lower zone and provided with freezing coils and with a receiver, a second evaporator located in the uppermost portion of the above-freezing zone and provided with a plurality of passes of coils located adjacent the side walls and back of the cabinet, the said evaporators being in unrestricted communication with each other, a motor compressor located in the lowermost portion of said cabinet on the outside, a preliminary cooling condenser connected directly to the outlet of the compressor and leading back to the top of the motor compressor housing, a main condenser connected to a top outlet of the motor compressor housing and connected at its other end to a restrictor, said restrictor leading to the inlet of the lowermost evaporator, conduits connecting the lowermost evaporator to the coils of the upper evaporator and a conduit connecting the upper evaporator with said receiver, a suction conduit leading from said receiver to the compressor inlet, a bypass conduit extending from said top outlet to the evaporator inlet, electric heater means in heat exchange relation with said receiver and with the refrigerant therein, valve means for normally closing said by-pass and electrical control means for simultaneously energizing said receiver heater, for opening said valve in said bypass and for running the motor compressor, the motor compressor pumping hot gaseous refrigerant directly from the compressor to said evaporator continuously and receiving hot gaseous refrigerant from said receiver continuously, the hot gaseous refrigerant being passed through the evaporators in heat exchange relation with the coils of said evaporators and with the frost carried by said evaporators on the exterior surfaces thereof to melt the accumulated frost, the defrosting action being continued until the frost has been removed to a desired degree, said electrical control means also including a thermostatic switch controlled by a bulb located adjacent the said receiver and its heater for cutting out the heater when the adjacent parts of the receiver and evaporator reach a predetermined heated temperature to prevent overheating of the lower evaporator and to terminate the defrost in such event.

8. In a defrosting system, an insulated cabinet having a cooling evaporator for a food Storage zone and a colder freezer evaporator for a below-freezing zone, a receiver carried by said freezer evaporator, said evaporators and receiver having connecting tubing in unrestricted communication with each other, a compressor, a condenser, and a capillary tube connected in this order, said capillary tube being connected to said freezer evaporator, which is connected to said cooling evaporator, and said cooling evaporator being connected to said receiver, a suction tube from an upper part of said receiver to said compressor, and a by-pass tube from said compressor to said freezer evaporator, by-passing said condenser and capillary tube, a solenoid valve biased to closed position in said by-pass tube, a thermostatic cold control switch having a bulb, controlling said compressor responsive to temperature of one of said evaporators, an electric heater in heat conducting contact with said freezer evaporator and receiver, heating the colder evaporator, which gathers more frost, and vaporizing and heating the refrigerant in said receiver, electrical control means for energizing said heater and solenoid valve simultaneously, the heater heating the freezer evaporator and its thermostatic switch bulb, causing the compressor to run and to deliver the hottest refrigerant rst to the freezer evaporator, having the most frost, and thence to the other warmer evaporator having the least frost, and back to the receiver and compressor to melt all the frost off the evaporators in a minimum amount of time, before the temperature of products in the cabinet is materially affected by the heat, said electrical control means including an electrical timer motor having a cam actuated switch controlled thereby for closing the circuit to said heater and solenoid at a predetermined time and opening the circuit after a predetermined interval of defrosting.

9. In a defrosting system, an insulated cabinet having a cooling evaporator for a food storage zone and a colder' freezer evaporator for a below-freezing zone, a receiver carried by said freezer evaporator, said evaporators and receiver having connecting tubing in unrestricted communication with each other, a compressor, a condenser, and a capillary tube connected in this order, said capillary tube being connected to said freezer evaporator, which is connected to said cooling evaporator, and said cooling evaporator being connected to said receiver, a suction tube from an upper part of said receiver to said compressor, and a by-pass tube from said compressor to said freezer evaporator, by-passing said condenser and capillary tube, a solenoid valve biased to closed position in said by-pass tube, a thermostatic cold control switch having a bulb, controlling said compressor responsive to temperature of one of said evaporators, an electric heater in heat conducting contact with said freezer evaporator and receiver, heating the colder evaporator, which gathers more frost, and vaporizing and heating the refrigerant in said receiver, electrical control means for energizing said heater and solenoid valve simultaneously, the heater heating the freezer evaporator and its thermostatic switch bulb, causing the compressor to run and to deliver the hottest refrigerant first to the freezer evaporator, having the most frost, and thence to the other Warmer evaporator having the least frost, and back to the receiver and compressor to melt all the frost off the evaporators in a minimum amount of time, before the temperature of products in the cabinet is materially affected by the heat, said electrical control means including an electrical timer motor having a cam actuated switch controlled thereby for closing the circuit to said heater and solenoid at a pre determined time and opening the circuit after a predetermined interval of defrosting, the said system including a thermostat having its controlling bulb in heat conducting contact with said freezer evaporator, and said thermostat being arranged to open the circuit to said heater and solenoid when its bulb is heated to a predetermined temperature.

l0. In a defrosting system, an insulated cabinet having a cooling evaporator for a food storage zone and a colder freezer evaporator for a below-freezing zone, a receiver carried by said freezer evaporator, said evapoators and receiver having connecting tubing in unrestricted communication with each other, a compressor, a condenser, and a capillary tube connected in this order, said capillary tube being connected to said freezer evaporator, which is connected to said cooling evaporator, and said cooling evaporator being connected to said receiver, a suction tube from an upper part of said receiver to said compressor, and a by-pass tube from said compressor to said freezer evaporator, by-passing said condenser and capillary tube, a solenoid valve biased to closed position in said by-pass tube, a thermostatic cold control switch having a bulb, controlling said compressor responsive to temperature of one of said evaporators, an electric heater in heat conducting contact with said freezer evaporator and receiver, heating the colder evaporator, which gathers more frost, and vaporizing and heating the refrigerant in said receiver, electrical control means for energizing said heater and solenoid valve simultaneously, the heater heating the freezer evaporator and its thermostatic switch bulb, causing the compressor to run and to deliver the hottest refrigerant first to the freezer evaporator, having the most frost, and thence to the other warmer evaporator having the least frost, and back to the receiver and compressor to melt all the frost off the evaporators in a minimum amount of time, before the temperature of products in the cabinet is materially affected by the heat, said electrical control means including an electrical timer motor having a cam actuated switch controlled thereby for closing the circuit to said heater and solenoid at a predetermined time and opening the circuit after a predetermined interval of defrosting, the said System including a thermostat having its controlling bulb in heat conducting contact with said freezer evaporator, and said thermostat being arranged to open the circuit to said heater and solenoid when its bulb is heated to a predetermined temperature, said latter thermostat bulb having a bellows connected to said bulb by a capillary tube, said capillary tubing being located in heat conducting relation with the tubes extending between the two evaporators and the header and being charged with a small amount of gas so that the bellows will not be actuated until all of the bulb and capillary tube are warmed from defrosting to insure the melting of the ice from both evaporators and all tubes.

11. In a defrosting system, an insulated cabinet having a cooling evaporator for a food storage zone and a colder freezer evaporator for a below-freezing zone, a receiver carried by said freezer evaporator, said evaporators and receiver having connecting tubing in unrestricted communication with each other, a compressor, a condenser, and a capillary tube connected in this order, said capillary tube being connected to said freezer evaporator, which is connected to said cooling evaporator, and said cooling evaporator being connected to said receiver, a suction tube from an upper part of said receiver to said compressor, and a by-pass tube from said compressor to said freezer evaporator, by-passing said condenser and capillary tube, a solenoid valve biased to closed position in said by-pass tube, a thermostatic cold control switch having a bulb, controlling said compressor responsive to temperature of one of said evaporators, an electric heater in heat conducting contact with said freezer evaporator and receiver, heating the colder evaporator, which gathers more y20 frost, and vaporizing and heating the refrigerant in said receiver, electrical controlmeans for energizing said heater and solenoid valve simultaneously, the heater heating the freezer evaporator and 'its thermostatic switch bulb, causing the compressor to run andl to deliver the hottest refrigerant first; tothe freezer evaporator, having the most frost, and thence tothe other warmer evaporator having the least frost, and back to the receiver and compressor to melt all the frost oif the evaporators in a minimum amount oftime, before the temperature of products in the cabinet is materially aifected by the heat, said electrical control means including an electrical timer motor having a cam actuated switch controlled thereby for closing the circuit to said heater and `solenoid at a predetermined time and opening the circuit after a predetermined interval of defrosting, said control means including reducing gearing driving a cam and including a driving pawl and ratchet, and an indicating knob indicating the time in hours, said control means being capable of being advanced ahead of said pawl by said knob to control defrosting or nondefrosting or the length of defrosting period manually.

References Cited in the le of this patent UNlTED STATES PATENTS `1,912,841 Haymond June 6, 1933 1,913,433 lDoble June 13, 1933 2,281,770 Hoesel May 5, 1942 2,526,379 Maseritz Oct. 17, 1950 2,548,324 Smith Apr. 10, 1951 2,592,394 Cochran Apr. 8, 1952 

